DRAFT : | nd Vertical mixing is inhibited at the thermocline due to the stability associated with the rapid increzse in density with depth. Vertical mixing requires the vertics1 novement of parcels of water. where vertical density gradicnts are great, as they are in the thermocline, these movements involve relatively large amounts of energy and are therefore less probable. Mixing, therefore, is less.3 In the wIGWJAM opera- tion (deep underwater atomic detonation off California) radio- activity was materially concentrated in thin stratified layers of high stability. These sheets of radioactive water had horizontal dimensions measured in miles and tens cf niles with vertical thickness of only a few meters (except above the thermocline). Contamination existed in the depth of the 4 thermocline and below it at (VIGVA4 because it was introduced at these levels. This is contrasted with fallout which is spread on the surface and remains mostly above the thermocline, but sIGVYAN is the best known example to illustrate the degree of stratification of waters ot layers of high stability. Computations cf stability have been made for the data taken on the HORIZON's cruise in the PPG erea. Fig. 11 shows the average stability of the wost stable 25 uete> leyer, and Fige 12 fives the cepth of the layer. -— 3- = ef le -— =e we ere ee — The stability values ee we Pehle le Since the downward penetration of radioactivity in solution in the water is very slow at the thermocline, sunmarines may generally avoid water with high activity by diving into the middle of the thermocline. Surface vessels muy obtain rele- tively clean water for their evaporators by punping water from within the thermocline depth zone. With a depressor on the end of a water line the latter might be acecmplished at normal speed. (At early times or during fallout, clean water undoubtedly exists in a ship's wake; therefore, a ship probably may obtain clean water for wash-Jown by traveling in a wide circle, or by following another vessel4 at some distance. - Isaacs.) ~ C ae